Use of carbon-13 substituent chemical shifts to scale non-hydrogen-bonding dipolar interactions of protonic solvents

B. Chawla, S. K. Pollack, C. B. Lebrilla, M. J. Kamlet, R. W. Taft

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Abstract

The aromatic 13C NMR shifts induced by protonic solvents in very dilute solutions of benzotrifluoride and phenylsulfur pentafluoride provide a novel means of scaling the dipolar character of these bulk solvents with little or no effects from solute-solvent hydrogen bonding. That is, these shifts have been utilized to define π solvatochromic parameters for 17 (OH, NH, and CH) protonic solvents. These results agree with previously obtained values for the strongly self-associated alcohols. However, for other more weakly self-associated solvents, evidence is presented that the method gives more reliable π values and provides the means for scaling hydrogen-bond donor abilities (α values) of relatively strong protonic solvents. The widely varying sensitivities (s) to solvent dipolarity of the para-carbon atom substituent chemical shifts for monosubstituted benzenes are determined by both the substituent-induced polarization of the benzene π electrons and by the substituent π-electron delocalization to or from the ring. This is shown by a unique DSP correlation of the s values.

Original languageEnglish (US)
Pages (from-to)6924-6930
Number of pages7
JournalJournal of the American Chemical Society
Volume103
Issue number23
StatePublished - 1981

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ASJC Scopus subject areas

  • Chemistry(all)

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